With an recent advances in the electronic industry, connection of conductors, and mounting of capacitors and IC chips has become more important.
Soldering (or brazing) has heretofore been used in the field of electronic industry. In order to perform bonding in a good manner, flow soldering methods such as dipping method, in-liquid dipping method, ultrasonic dipping method and reflow soldering methods such as infrared method, heated air blowing method, electric resistor method, ultrasonic method, laser method and high frequency induction method have been recently used as well as copper soldering method.
Since laser soldering is capable of condensing laser lights in a fine spot in this case, it has advantage in that it can preferably cope with the miniaturization of electronic devices and elements and the output can be easily electrically or optically controlled. There is also an advantage that no inclusion of an impurity in the solder occurs since the laser method is a non-contact method for the solder.
In accordance with the non-contact laser method, a formed solder 3 is irradiated with laser lights L on the surface thereof when a member 2 to be bonded, for example, a conductor is soldered to a base material 1 with the formed solder 3.
Since the reflection factor of the surface of the solder 3 for the laser lights is high, the absorption factor for the laser lights is low. Therefore, it is necessary to emit laser lights at a high power. This invites an increase in the scale of a power source for a laser light generator, etc.
Elevation in temperature of a member 2 to be bonded is mainly due to thermal conduction from the solder 3. Accordingly, the speed of the temperature elevation is low, resulting in an decrease in soldering speed.
The laser lights abruptly decrease their energy after they are emitted into air from an emitting position. Most of the energy will be lost by reaching an irradiation position.
Although the laser lights have a high converging ability, they have a diverging ability to some extent. Accordingly, they will heat a member, for example, a portion of the base material, which is not desired to be heated as shown in FIGS. 27 and 28 so that it may be thermally damaged.
It is therefore a main object of the present invention to provide a soldering method which is capable of sufficiently performing a soldering at a low output and positively heating only an object in a position where it is desired to be heated.